Project 2 examines the contribution of murine and human gamma/delta (gd) T cells to the interface between the innate and adaptive immune responses. The studies by Dr. Huber's group on murine gd T cells in coxsackievirus B3 (CVB3) infection, and Dr. Budd's group on human gd T cells in Lyme arthritis following infection with Borrelia burgdorferi have made remarkably similar findings, gd T cells accumulate at sites of inflammation (joints in Lyme arthritis, hearts in CVB3 infection). The overall model based on the preliminary findings is that CVB3 and B. burgdorferi interact with specific Toll-like receptors (TLR) to induce members of the CD1 family and cytokines in a caspase-dependent manner (Aim 1). This results in the activation of gd T cells through their potential recognition of CD1 family members (Aim 2). The activated gd T cells then activate myeloid DC, which can then promote activation of naTve CD4 T cells (Aim 3). Finally, the intensity of TCR signaling by gd or ab CD4 T cells sets the level of caspase activity, which is required both to initiate cell cycling as well as subsequent contraction phase by cell death. The Specific Aims of this project are thus: Aim 1. Borrelia burgdorferi and coxsackievirus B3 (CVB3) infection induce CD1 family members on target cells in a TLR- and caspase-dependent manner. We will define the role of TLR signals in inducing CD1 expression, and the contribution of caspases to TLR signaling. Aim 2. Do certain gd T cell subsets recognize CD1 members? We will examine the ability of human and mouse gd T cells be activated in vitro by CD1, in vivo during CVB3 or Borrelia infection in the presence or absence of CD1. A soluble TCR-gd tetramer will be used to further define gd specificity. Aim 3. Do gd T cells activate DC, which promotes activation of naive CD4+ T cells. Aim 4. The intensity of TCR signaling by gd or ab CD4 T cells sets the level of intracellular caspase activity, which is required to initiate cell cycling and to regulate subsequent contraction by cell death. Significance: Borrelia burgdorferi is the major vector-borne disease in the U.S., and Coxsacievirus is a leading cause of cardiomypathy. gd T cells accumulate at sites of inflammation in both diseases and promote a Th1 cytokine response. Almost nothing is known regarding the specificity of gd T cells or their function at the interface between the innate and adaptive immune responses